Thermostat



George Forrest .Dra/fe MM,MM

ATTORNEYS Patented 9ct. 27, 1936 l UNIT-ED .STATES PATENT OFFICETHERMOSTAT George Forrest Drake, Rockford, Ill., assignor tov Howard D.Colman, Rockford, Ill.

Application January 3, 1933, Seria-l No. 649,897

12 Claims. '(Cl. 20o-139) This invention relates to improvements inFigure 1 is a front elevational view of a therthermostats and moreparticularly to those of mostat embodying the features of the presentthe so-called immersion type in which the therinvention, a portion ofthe cover being broken mo-sensitive element is enclosed by a protectingaway.

5 casing immersed in the iiuid the temperature Fig. 2 is a sectionalview taken along the line of which controls the thermostat. 2-2 of Fig.1.

vAs heretofore constructed. thermostats of In the form selected forpurposes of illustrathe above character have been characterized by tion,the invention is embodied in an immersion an objectionable lag infollowing the temperathermostat in which a thermo-sensitive element tureof the controlling fluid. An important ob- 3 disposed within animperforate protecting casm ject of the present invention is to overcomethis ing in the form of a metallic tube l actuates a objection byproviding for`y the rapid transfer control instrumentality such asswitches 5 and of Aheat between the thermostatic element and the 6 in.response to temperature changes of the protecting casing without at thesame time inuid to which the tube is exposed. As is gentroducingfriction or other resistance interiererally the case in thermostats ofthis kind, the ing with freedom of movement of the element. element 3comprises an .elongated strip of bi- In carrying out the foregoingobject, the inmetallic material coiled into the form of a helix ventioncontemplates the introduction intothe of a diameter. slightly less thanthe tube and protecting case of a body of liquid which rehaving the endadjacent the closed end of the mains fluid at the working temperature ofthe tube fastened to a head 1 on an elongated rod 20 thermostat andwhich provides a connection 8 and the other end secured to a head 9 onthe adapted to conduct heat rapidly between the end of a sleeve I0 ofsmallerdiameter than the casing and the thermostatic element. coil 3.The head 9 serves to support the inner The invention also resides inusing as the heatend of the sleeve concentric with the tube andconducting connection above referred to, a liqalso acts through themedium of the element 25 uid such as mercury which has a high boiling 3to maintain concentric relation. of the sleeve f point, low vaporpressure, high thermal conand rod. The element 3 is thus free to expandductivity and low thermal capacity. and contract under temperaturechanges.

A further object is to provide a novel means The end of the sleeveopposite the element 3 for sealing the mercury in the protectingcasprojects beyond the open end of the tube 4 30 ing of the thermostat.through an elongated insulating base Il in which An immersion thermostatis frequently subthe sleeve is snugly received. The correspondjected totemperatures varying widely from the ing end of the rod 8 projects fromthe sleeve temperature at which the thermostat is set to and is centeredtherein by a bushing I 2 closing respond with the result that thethermostatic the end of the sleeve while permitting freedom 35 elementbecomes strained to an objectionable of relative rotation between thesleeve and rod. degree and frequently damaged. It is also an Formed onthe base Il is a flange I3 which'iits object of the present invention toovercome this snugly into the open end of 'the tube 4 as the difficultyby employing a motion-transmitting base with the sleeve and rod mountedthereon 40 connection of novel construction adapted to are inserted inthe tube. 40 maintain any desired setting of the thermostat To providefor adjustment of the thermostat, but adapted to yield withoutdestroying such an arm 33 is fast on the outer end of the sleeve settingunder any abnormal temperatures and I0 and held in fixed positionrelative tcran adprevent damage to the thermostat element. y justinglever 34 by a spring 35 acting between Another object is to provide, ina thermostat pins 36 projecting from the arm and lever. Byv

having a detent device for obtaining a rapid shifting the leverlaterally, the angular position movement of the controlling arm betweentwo of the sleeve I0 within the base Il may be limit positions, a novelmeans by which the changed as desired. A spring 31; acting betweentemperature differential to which the thermoa collar 38, and a sleeve 39in which the sleeve stat responds maybe varied as desired without l0 isjournaled serves to maintain proper axial affecting the operation of thedetent device.` relation of the parts while permitting removal Otherobjects and advantages of the invenof the base H and the parts carriedthereby tion will become apparent from the following from the tube I.detailed description taken in connection with The present inventioncontemplates the use of me accompanying drawing, in which. a quantity uof liquid heat-conducting medium 55 within the tube I immersing at leasta part of the thermostatic element 3 so as to form a connection betweenthe element and the tube capable of conducting heat between the tworapidly without introducing friction or otherwise decreasing thesensitivity of the thermostat. Preferably, the level of the liquid isbelow the sleevev Ill when the latter is disposed in horizontalposition. Mercury is ideally suited for this purpose, tlrst because itremains liquid over the range of temperatures for which immersionthermostats are ordinarily used, and secondly because its low vaporpressure avoids any substantial loss by evaporation in service use.Because of its metallic character, mercury possesses high thermalconductivity and low heat capacity both of which render the thermostatextremely sensitive. A thermostat constructed in accordance with thepresent invention will follow temperature changes in a water bath nearlyas rapidly as when the thermostatic element is immersed directly in thebath.

The use of mercury as the heat conducting medium necessitates making allof the parts with which it contacts of material such as iron and ferrousalloys with which mercury does not form an amalgam. Provision is alsomade for sealing the tube 4 against the escape of the mercury. Hereinthis may be accomplished by a plug consisting of washers I5 composed ofyieldable material such as cork tting snugly around the sleeve and inthe tube and retained between the head 9 and a clamping collar I6. Theplug thus formed will slide readily in the tube and will eiectuallyprevent escape ot the mercury along the inner wall of the tube.

T0 facilitate assembly of the thermostat, it is preferred to introducethe mercury after mounting oi the sleeve I0 and the rod B upon the baseII. For this purpose, an aperture I1 through which the mercury may bepoured is formed in` the sleeve preferably in the upper portion thereofbetween the plug I5 and the base II. In assembly of the thermostat, thetube I is first screwed into the wall on which it is to be mounted andthe thermostatic element and sleeve assembly inserted in the open end ofthe tube until the plug I5 enters such end, the hole I1 being disposedoutside of the tube and at the top of the sleeve. A quantity of mercurysuilicient to cover the lower portion of the element 3 is then pouredthrough the hole and allowed to flow down the sleeve III beyond the end.thereof. The

bushing I2 prevents flowing of the mercury out of the other endof thesleeve during the iilling operation. Then the sleeve is pushed fartherinto the tube, the flange I3 finally becoming seated in the tube withthe base I I in upright position. The mercury is thus trapped in thetube beyond the plug I5 and remains in this space so long as theposition of the thermostat is not disturbed.

The control instrumentality which, as above set in a manner such as topermit of a substantial yielding of the connection upon continuedexparisien or contraction of the thermostatic coil 3 after the tonguehas engaged one or the other of the contacts I9, and this, withoutdestroying the setting of the thermostat for response to temperaturechanges relative to a predetermined value. To this end, the tongue issupported at its lower end by and loosely pivoted on a bushing 20 faston the forwardly projecting end of the rod 8. Mounted on the tongue toswing laterally about axes extending parallel to the tongue axis are twolevers in the form of bars 2| and 22 fulcrumed intermediate their endson the ends of lugs 23 rigid with and projecting laterally from thetongue intermediate the ends of the latter. At their upper ends, thebars 2I and 22 are joined by a contractile spring 24 which normallytends to swing the bars against opposed stops 25 formed by a strap 25rigid with the hub of the tongue. The tongue and the levers supportedthereon when in engagement with the stops 25 thus constitute a unitwhich is swingable about the tongue axis.

Angular movements of the rod l are imparted to the unit above referredto through the medium of oppositely acting one-way connections with thelevers 2I and 22. To form these connections, an arm 21 clamped on andthereby made fast to the outer end o! the bushing 20 carries two stops28 which are disposed externallyof the barsZI and 22 for engagement withthese bars adjacent the stops 25. The stops 28 are formed by screwsthreading into the arm 21 so that the degree oi lost-motion between thearm and the tongue unit may be varied as desired;

If the stops 28 are spaced the same distance apart as the stops 25,there will be no lost motion in the motion-transmitting connection, andthe levers 2l and 22 will each engage their stops 25 and 28 when theexisting temperature tends to maintain the tongue between the contactsI9. If now a wide variation in temperature occurs swinging the arm 21clockwise, the arm acting on the lever 22 will move the tongue and leveras a unit in the same direction until the switch 5 is closed, the levex22 being maintained against its stop 25 owing tothe fact that theresiliency of the spring 2l is then slightly greater than that of thethermostatic coil. Then as the tempera'ture change increases and thestress developed in the coil 3 is suiiicient to overcome the spring 24,the arm 21 continues to move while the tongue remains stationary. Thismovement is permitted by swinging of the lever 22 about its Iulcrumwhich may, owing to the permissible movement of the lever 22, continueover a wide range of temperature change. Then as the arm 21 movesreversely, the lever 22 is allowed to swing back toward its stop 25, thetongue maintaining the switch 5 closed until the stop is engaged by thelever and the tension in the thermostatic element decreased below thatoi the spring 24.

iid

Another advantage of the present yleldable connection is that it permitsthe use of a magnetic detent or over-center device 29 for avoidingchattering of the thermostat tongue while at the same time permittingthe range of temperature change required for opening one switch andclosing the other to be increased as may be desired. The device 29comprises a magnet having two poles 30 with faces 3l of equal areadisposed on opposite sides oi the tongue'h i8, the upper end portion ofwhich constitutes the magnet armature. The iaces 3i are spaced apart agreater distance than the contacts I9. With this arrangement, anattractive force will be exerted on the tongue according to the locationof the tongue relative to the center of the gap between the pole facesso that the tongue will remain against one of the contacts IS until theattractive force maintaining this position is overcome whereupon thetongue will be moved with a quick snap action against the other contact.f

lit is often necessary in practice to render a thermostat of the presentcharacter responsive only to a relatively wide temperature differentialwhich is generally accomplished `by increasing the spacing of thecontacts I9. Such a change would prevent proper operation oi themagnetic detent but is rendered possible by adjustment of the yieldableconnection above described. To thus increase thedesired temperaturediierential, the screws 28 are backed away from the -levers 2t and 22 toprovide lost-motion in the motion-transmitting connection permittingsome degree of movement oi, the arm v2li independently of the tongue andlever unit. In this way, response of the thermostat to any desiredtemperature/difierential may be obtained without in any way affectinglthe operation of the magnetic detent.

I claim as my invention:

` l. in immersion thermostat combining an elongated tube closed at oneend, a sleeve pro-lv jecting into said tube, a rod extending throughsaid sleeve beyondthe inner end of the latter, an elongated strip ofbimetallic metal within said tube spirally coiled around the inner endof said rod and having opposite 'ends secured to the sleeve and rodrespectively, a plug surrounding and secured to.- said sleeve adjacentsaid strip and adapted to be received in said tube snugly upon insertionof the rod and sleeve, and a hole in said sleeve disposed between saidplug and the outer end of the sleeve so as to be located outside oi saidtube upon insertion oi the sleeve until said plug enters the open end ofthe tube, said sleeve serving upon the pouring of liquid into said holeto conduct such liquid into the space between said plug and the closedend oi the tube.

2. .an immersion thermostat combining 'an elongated tube closed at oneend, asleeve projecting into said tube. a rod extending throughl saidsleeveibeyond the inner end of the latter, an elongated strip oibimetallic metal within said tube spirally coiled around the innerendioi said rod and having opposite ends secured to the sleeve and rodrespectively, a plug surrounding and secured to said sleeve adjacentsaid strip and adapted to be received in said tube snugly upon insertionof the rod and Sleeve, a hole in said sleeve disposed between said plugand the outer end oi' the sleeve so as to be located outside ci said`tube and at the top of the latter upon partial insertion o! said sleevewith the tube disposed horizontally and said sleeve and tube in apredetermined angular relation, said sleeve serving, upon the pouring ofliquid through said hole, to conduct the liquid into the space `1betweenthe plug` and the closed end of said tube,

and means acting to prevent the ilow of said liquid through said sleevein the opposite direction while permitting freedom of relative movementbetween said sleeve and rod.

3. A thermostat combining a control member mounted for movement inopposite directions between twolimit positions, opposed stopsdetermining said positions, two independently operable levers fulcrumedon said member, spring means normally acting to swing said levers inopposite directions relative to said member, means for limiting suchvnfiovemcnts-.ot the levers, a thermostatic ly actuated element movablein opposite directi ns in response to rises and falls in temperaturerelative to a predetermined value, and oppositely acting one-way.connections between said element 'and the respective', levers, eachoperable upoii movement of saidlelement in one direction to move one ofsaid levers and said member as a unit until one of saidstops is engagedf by the member and then to move the lever relative to the memberagainst the action of said spring means.

4. A thermostat combining a control member mounted for movement inopposite directions between two limit positions, opposed stops deterwmining said positions, two independently operable Y levers fuicruxned onsaid membenspring means member and `then to move the lever relative tolthe member against the action oi said spring means, said memberproviding a. flat magnetic armature adjacent said stops, and a magnetpro viding two oppositely facing closeltr spaced magnetic polesonopposite sides oiv said armature, each oi saidy connections beingadjustable to vary the amount oi lost motion between said element andsaid levers whereby to change .the degree of sensitivity of thethermostat without affecting the action of said magnet upon saidarmature.

5. A thermostat combining a pair of closely spaced stops, a controlmember movable in opposite directions into engagement with therespective stops and having. opposed stops rigidtherewith, twoindependently operable levers Iulcrumed on said memben'means on saidmember directions, spring Imeans normally urging the re spective leversinto engagement with said limiting means,' a thermostatic eiementanactuating member arranged to be moved in opposite directions by saidelement and having one-way connections with the respective levers, eachoi said connections operating upon movement of the actuating member inone direction to move said control member and one lever as a unit intoengagement with one oi said stops and then to move such lever relativeto the control member.

6. Athermostat combining a stop, an elongated dit ' limiting themovements of said levers in opposite tudinally of and pivoted on saidarm to swing about an axis located intermediate the ends of the arms andextending substantially parallel to said rst mentioned axis, springmeans acting on said lever to swing the latter in one direction relativeto said arm, means on said arm limiting the movement of the lever bysaid spring means, a thermostatic element, a member actuated by `saidelement and engaging said lever whereby,

upon movement in one direction, to swing said lever and arm as a unitabout said ixed axis until said stop is engaged by the arm and then tomove said lever relative to the arm and away from said limiting means.

7. A thermostat combining a stop, an elongated arm mounted to swingabout a xed axis toward and away from said stop, a lever pivoted on saidarm to swing about an axis spaced a substantial distance from andextending substantially parallel to said first mentioned axis, springmeans acting on said lever. to swing the latter in one directionrelative to said arm, means on said arm limiting the movement of thelever by said spring means, a thermostatic element, a member actuated bysaid element and engaging said lever whereby, upon movement in onedirection, to swing said lever and arm as a unit about said xed axisuntil said stop is engaged by thearm and then to move said leverrelative to the arm and away from said limiting means.

8. A thermostat combining a stop, an elongated arm mounted to swingabout a xed axis toward and away from said stop, a lever pivoted on saidarm to swing about an axis spaced Va substantial distance trom andextending substantially parallel to said first mentioned axis, springmeans acting on said lever to swing the latter in one direction relativeto said arm, means on said arm limiting the movement of the lever bysaid spring means, a thermostatic element, a. member actuated by saidelement and having an adjustable one-way connection with said leveroperable upon movement of the member in one direction to swing said armand lever as a unit until said stop is engaged and then to move thelever relative to the arm.

9. A thermostat combining a xed contact, a contact arm movable into andout oi' contacting engagement therewith, a stop on said arm, a leverfulcrumed on said arm and resiliently urged about its fulcrum towardsaid stop, a thermostatic element, an actuating member movable inopposite directions by said element and operable upon continued movementin one direction to move said arm through the medium of said lever untilthe arm engages said contact and then to move the lever away from saidstop, said member, upon reverse movement, permitting movement of thelever against said stop before retraction of said arm away from saidcontact.

l0. `A control instrument comprising, in com bination, a pair of closelyspaced stationary stops, a movable contact disposed between said stopsand cooperating with one of the stops to form a antenas' control switch,an operating shaft, a sensitive ac tuating element for said shaft havinga normal range of operation determined by the .spacing of said stops,and a motion-transmitting device between said shaft .and said movablecontact, said device including a part carrying said movable contact andloosely supported by said shaft, another part movable by said actuatingelement and extending substantially parallel to the first part inlaterally offset relation to the axis of said shaft, and spring meansacting to hold said parts in a normal predetermined relation formovement in unison while said movable contact moves between said stopsbut permitting relative movement between the parts in oppositedirections from said normal relation uponmovement of the actuatingelement beyond its said normal range of operation in oppositedirections.

11. A control instrument comprising, in combination, an operating shaft,a thermostatic actuat ing element having one end normally heldstationary and the other end vconnected to said shaft toactuate thesame, an arm mounted to turn on said shaft and carrying a movablecontact, a pair of stops acting to limit the movef ment thereof and onecooperating with said contact to fornr an' electric switch, and a devicefor transmitting motion from said shaft to said arm including a secondarm fixed on the shalt and having a part offset laterally from the ilrstarm and from the axis oi.' the shaft, and spring means acting to holdsaid two arms in a normal predetermined relation for movement in unisonwhile said movable contact is moved between said stops,

but permitting relative movement between the two arms in oppositedirections from said normal position upon movement of the actuatingelement beyond the normal range of operation in either directiondetermined by the spacing of said stops.

l2. An insertion thermostat comprising a controlling switch mechanismhaving a housing, an operating shaft projecting from the housing, and ahelicaliy coiled thermostatic actuating element encircling the end ofthe shaft opposite said housing, said actuating element being oi! alength substantially less than the length of said shaft and having oneend secured to the projecting end of the shaft and its other endconnected with said housing so as to be held against movement, a tubularmetallic casing having an open end'removably secured to said housing andan opposite closed end whereby to enclose completely l'said shaft andactuating element with the latter spaced from the inner peripheral wallof the casing, said casing providing when disposed honzontally atrough-like receptacle of a length cor responding approximately to thelength of4 said actuating element and adapted to contain s, heatconducting element in liquid form in a quantity suilicient to i111 thespace between the actuating element and the casing, and means adaptedwhen said actuating element is partially inserted into said casing toconduct said liquid into said trough-like receptacle, GEORGE FORRESTBRAKE.

